Pulse oximeters are medical
devices used to measure the oxygen level (or oxygen
saturation) in the blood. Pulse oximeters are considered to
be a noninvasive, painless, general indicator of oxygen
delivery to the tissues (e.g.,
finger,
earlobe,
forehead, toe or nose).

Oxygen in the air is
breathed into the lungs. The oxygen then passes into the
blood where the majority of the oxygen attaches to
hemoglobin (a protein located inside the red blood cell) for
transport in the bloodstream. The oxygenated blood
circulates to the tissues.

Pulse oximeter technology
utilizes the light absorptive characteristics of hemoglobin
and the pulsating nature of blood flow in the arteries to
aid in determining the oxygenation status in the body.
First, there is a color difference between arterial
hemoglobin saturated with oxygen, which is bright red, and
venous hemoglobin without oxygen, which is darker.

Second, with each pulse or
heartbeat there is a slight increase in the volume of blood
flowing through the arteries. Because of the increase of
blood volume, albeit small, there is an associated increase
in oxygen-rich hemoglobin. This represents the maximum
amount of oxygen-rich hemoglobin pulsating through the blood
vessels.

A clip-like device called a
probe is placed on a body part, such as a
finger or ear lobe, to
measure the blood that is still carrying or is saturated
with oxygen. The probe houses a light source, a light
detector, and a microprocessor, which compares and
calculates the differences in the oxygen-rich versus
oxygen-poor hemoglobin. One side of the probe has a light
source with two different types of light, infrared and red,
which are transmitted through the finger to the light
detector side of the probe.
SPO Medical
pulse oximeters use
reflectance technology to measure oxygen saturation.
The oxygen-rich hemoglobin absorbs more of the infrared
light and the hemoglobin without oxygen absorbs more of the
red light. The microprocessor calculates the differences and
converts the information to a digital readout. This
information helps the physician assess the amount of oxygen
being carried in the blood and evaluate the need for
supplemental oxygen.

The respiratory system
is made up of the organs involved in the interchanges of
gases, and consists of the:

nose

pharynx

larynx

trachea

bronchi

lungs

The upper respiratory
tract includes the:

nose

nasal cavity

ethmoidal air cells

frontal sinuses

maxillary sinus

larynx

trachea

The lower respiratory tract
includes the lungs, bronchi, and alveoli.

What are the functions
of the lungs?

The lungs take in oxygen,
which cells need to live and carry out their normal
functions. The lungs also get rid of carbon dioxide, a waste
product of the body's cells.

The lungs are a pair of
cone-shaped organs made up of spongy, pinkish-gray tissue.
They take up most of the space in the chest, or the thorax
(the part of the body between the base of the neck and
diaphragm).

The lungs are enveloped in
a membrane called the pleura.

The lungs are separated
from each other by the mediastinum, an area that contains
the following:

the heart and its
large vessels

trachea (windpipe)

esophagus

thymus

lymph nodes

The right lung has three
sections, called lobes. The left lung has two lobes. When
you breathe, the air enters the body through the nose or the
mouth. It then travels down the throat through the larynx
(voice box) and trachea (windpipe) and goes into the lungs
through tubes called main-stem bronchi.

One main-stem bronchus
leads to the right lung and one to the left lung. In the
lungs, the main-stem bronchi divide into smaller bronchi and
then into even smaller tubes called bronchioles. Bronchioles
end in tiny air sacs called alveoli.

Reasons to use Pulse
Oximeters

Pulse oximeters may be used
to assess the adequacy of oxygen levels (or oxygen
saturation) in the blood in a variety of circumstances such
as surgery, other procedures involving sedation (e.g.,
bronchoscopy), adjustment of supplemental oxygen as needed,
effectiveness of lung medications, and patient tolerance to
increased activity levels. Other reasons may include, but
are not limited to, the following:

Pulse oximetry is a quick,
noninvasive method of measuring oxygen saturation in the
blood. Risks associated with using a pulse oximeter are
minimal and rare.

Prolonged application of
the probe may cause tissue breakdown at the application
site. Skin irritation may result from the adhesive used in
adhesive-containing probes.

Use of pulse oximeters in
cases of smoke or carbon monoxide inhalation is
contraindicated, because oximetry cannot distinguish between
normal oxygen saturation in the hemoglobin and the
carboxyhemoglobin saturation of hemoglobin that occurs with
inhalation of smoke or carbon dioxide.

There may be other risks
depending upon your specific medical condition. Be sure to
discuss any concerns with your physician prior to the
procedure.

Certain factors or
conditions may interfere with the results of the test. These
include, but are not limited to, the following:

decreased blood flow
to the peripheral vessels

light shining directly
on the oximetry probe

movement of the area
to which the probe is attached

severe anemia
(decreased red blood cells)

extreme warmth or
coolness of the area to which the probe is attached

recent injection of
contrast dye

smoking tobacco

Function

A
blood-oxygen monitor displays the percentage of
arterial
hemoglobin in the
oxyhemoglobin configuration. Acceptable normal
ranges are from 95 to 100 percent, although values
down to 90% are common. For a patient breathing room
air, at not far
above sea level, an estimate of arterial pO2 can
be made from the blood-oxygen monitor SpO2 reading.

A
pulse oximeter is a particularly convenient
noninvasive measurement instrument. Typically it
has a pair of small
light-emitting diodes (LEDs) facing a
photodiode through a translucent part of the
patient's body, usually a fingertip or an earlobe.
One LED is red, with
wavelength of 660 nm, and the other is
infrared, 905, 910, or 940 nm. Absorption at
these wavelengths differs significantly between
oxyhemoglobin and its deoxygenated form; therefore,
the oxy/deoxyhemoglobin ratio can be calculated from
the ratio of the absorption of the red and infrared
light. The absorbance of oxyhemoglobin and
deoxyhemoglobin is the same (isosbestic
point) for the wavelengths of 590 and 805 nm;
earlier oximeters used these wavelengths for
correction for hemoglobin concentration.[2]

The monitored signal bounces in time with the
heart beat because the arterial
blood vessels expand and contract with each
heartbeat. By examining only the varying part of the
absorption spectrum (essentially, subtracting
minimum absorption from peak absorption), a monitor
can ignore other tissues or nail polish, (though
black nail polish tends to distort readings)[3]
and discern only the absorption caused by arterial
blood. Thus, detecting a pulse is essential to the
operation of a pulse oximeter and it will not
function if there is none.

A
pulse oximeter is useful in any setting where a
patient's
oxygenation is unstable, including
intensive care, operating, recovery, emergency
and hospital ward settings,
pilots in unpressurized aircraft, for assessment
of any patient's oxygenation, and determining the
effectiveness of or need for supplemental
oxygen. Assessing a patient's need for oxygen is
the most essential element to life; no human life
thrives in the absence of oxygen (cellular or
gross). Although a pulse oximeter is used to monitor
oxygenation, it cannot determine the metabolism of
oxygen, or the amount of oxygen being used by a
patient. For this purpose, it is necessary to also
measure
carbon dioxide (CO2) levels. It is possible that
it can also be used to detect abnormalities in
ventilation.

However, the use of a pulse oximeter to detect
hypoventilation is impaired with the use of
supplemental oxygen, as it is only when patients
breathe room air that abnormalities in respiratory
function can be detected reliably with its use.
Therefore, the routine administration of
supplemental oxygen may be unwarranted if the
patient is able to maintain adequate oxygenation in
room air, since it can result in hypoventilation
going undetected.

Because of their simplicity and speed, pulse
oximeters are of critical importance in
emergency medicine and are also very useful for
patients with respiratory or cardiac problems,
especially
COPD, or for diagnosis of some
sleep disorders such as
apnea and
hypopnea. Portable battery-operated pulse
oximeters are useful for pilots operating in a
non-pressurized aircraft above 10,000 feet (12,500
feet in the US)[4] where
supplemental oxygen is required. Prior to the
oximeter's invention, many complicated
blood tests needed to be performed. Portable
pulse oximeters are also useful for mountain
climbers and athletes whose oxygen levels may
decrease at high
altitudes or with exercise. Some portable pulse
oximeters employ software that charts a patient's
blood oxygen and pulse, serving as a reminder to
check blood oxygen levels.

Oximetry is not a complete measure of respiratory
sufficiency. A patient suffering from
hypoventilation (poor
gas exchange in the
lungs) given 100% oxygen can have excellent
blood oxygen levels while still suffering from
respiratory acidosis due to excessive carbon
dioxide.

It
is also not a complete measure of circulatory
sufficiency. If there is insufficient
bloodflow or insufficient hemoglobin in the
blood (anemia),
tissues can suffer
hypoxia despite high
oxygen saturation in the blood that does arrive.

A
higher level of
methemoglobin will tend to cause a pulse
oximeter to read closer to 85% regardless of the
true level of oxygen saturation. It also should be
noted that the inability of two-wavelength
saturation level measurement devices to distinguish
carboxyhemoglobin due to
carbon monoxide poisoning from oxyhemoglobin
must be taken into account when diagnosing a patient
in emergency rescue, e.g., from a fire in an
apartment. A Pulse
CO-oximeter measures absorption at additional
wavelengths to distinguish CO from O2 and determines
the blood oxygen saturation more reliably.

According to a report by Frost & Sullivan entitled
U.S. Pulse Oximetry Monitoring Equipment Market, US
sales of oximeters were worth $201 million in 2006.
The report estimated that oximeter sales in the US
would increase to $310 million annually by 2013.[5]

In
2008, more than half of the major
internationally-exporting medical equipment
manufacturers in
China were producers of pulse oximeters.[6]

In
June, 2009,
video game company
Nintendo announced an upcoming
peripheral for the
Wii console, dubbed the "Vitality
Sensor," which consists of a pulse oximeter.
This marks the onset of the use of this device for
non-medical, entertainment purposes.[